How did you test? Did you log the frequency while playing?
I most certainly did, I was using TechPowerUp GPU-z.
Here's an excerpt, but it goes on like this pretty much during the whole play session:
Date , GPU Core Clock [MHz] , GPU Memory Clock [MHz] , GPU Temperature [°C] , GPU Load [%] , Memory Usage (Dedicated) [MB] , Memory Usage (Dynamic) [MB] ,
2012-07-05 21:26:50 , 600.0 , 800.0 , 76.0 , 70 , 29 , 213 ,
2012-07-05 21:26:51 , 750.0 , 800.0 , 76.0 , 78 , 29 , 212 ,
2012-07-05 21:26:52 , 800.0 , 800.0 , 77.0 , 66 , 29 , 212 ,
2012-07-05 21:26:53 , 700.0 , 800.0 , 76.0 , 58 , 29 , 213 ,
2012-07-05 21:26:54 , 1000.0 , 800.0 , 82.0 , 88 , 29 , 213 ,
2012-07-05 21:26:55 , 950.0 , 800.0 , 81.0 , 87 , 29 , 214 ,
2012-07-05 21:26:56 , 1000.0 , 800.0 , 81.0 , 90 , 29 , 214 ,
2012-07-05 21:26:57 , 950.0 , 800.0 , 82.0 , 86 , 29 , 214 ,
2012-07-05 21:26:58 , 1050.0 , 800.0 , 83.0 , 90 , 29 , 214 ,
2012-07-05 21:27:00 , 1050.0 , 800.0 , 82.0 , 88 , 29 , 214 ,
2012-07-05 21:27:01 , 1050.0 , 800.0 , 83.0 , 86 , 29 , 214 ,
2012-07-05 21:27:02 , 1050.0 , 800.0 , 84.0 , 87 , 29 , 214 ,
2012-07-05 21:27:03 , 950.0 , 800.0 , 83.0 , 88 , 29 , 214 ,
2012-07-05 21:27:04 , 1050.0 , 800.0 , 83.0 , 88 , 29 , 214 ,
2012-07-05 21:27:05 , 1050.0 , 800.0 , 82.0 , 75 , 29 , 212 ,
2012-07-05 21:27:06 , 1050.0 , 800.0 , 84.0 , 82 , 29 , 212 ,
2012-07-05 21:27:07 , 1050.0 , 800.0 , 83.0 , 80 , 29 , 212 ,
2012-07-05 21:27:08 , 1050.0 , 800.0 , 82.0 , 75 , 29 , 212 ,
2012-07-05 21:27:09 , 1050.0 , 800.0 , 84.0 , 78 , 29 , 212 ,
2012-07-05 21:27:10 , 1050.0 , 800.0 , 84.0 , 79 , 29 , 211 ,
2012-07-05 21:27:11 , 1000.0 , 800.0 , 84.0 , 80 , 29 , 211 ,
2012-07-05 21:27:12 , 1050.0 , 800.0 , 84.0 , 80 , 29 , 211 ,
2012-07-05 21:27:13 , 1050.0 , 800.0 , 85.0 , 80 , 29 , 211 ,
2012-07-05 21:27:14 , 1000.0 , 800.0 , 82.0 , 54 , 31 , 219 ,
2012-07-05 21:27:15 , 1050.0 , 800.0 , 83.0 , 78 , 31 , 219 ,
2012-07-05 21:27:16 , 1050.0 , 800.0 , 85.0 , 85 , 31 , 219 ,
2012-07-05 21:27:17 , 950.0 , 800.0 , 83.0 , 80 , 29 , 214 ,
2012-07-05 21:27:18 , 1000.0 , 800.0 , 83.0 , 71 , 29 , 215 ,
2012-07-05 21:27:19 , 950.0 , 800.0 , 83.0 , 71 , 29 , 215 ,
2012-07-05 21:27:20 , 850.0 , 800.0 , 82.0 , 70 , 29 , 215 ,
2012-07-05 21:27:21 , 850.0 , 800.0 , 81.0 , 75 , 29 , 215 ,
2012-07-05 21:27:22 , 800.0 , 800.0 , 79.0 , 56 , 29 , 224 ,
2012-07-05 21:27:23 , 650.0 , 800.0 , 79.0 , 65 , 29 , 224 ,
2012-07-05 21:27:24 , 750.0 , 800.0 , 78.0 , 70 , 29 , 231 ,
2012-07-05 21:27:25 , 350.0 , 800.0 , 78.0 , 40 , 29 , 231 ,
2012-07-05 21:27:26 , 650.0 , 800.0 , 76.0 , 42 , 29 , 231 ,
2012-07-05 21:27:27 , 600.0 , 800.0 , 77.0 , 45 , 29 , 231 ,
2012-07-05 21:27:28 , 350.0 , 800.0 , 77.0 , 40 , 29 , 231 ,
2012-07-05 21:27:29 , 350.0 , 800.0 , 75.0 , 40 , 29 , 231 ,
2012-07-05 21:27:30 , 350.0 , 800.0 , 75.0 , 44 , 29 , 232 ,
2012-07-05 21:27:31 , 350.0 , 800.0 , 76.0 , 47 , 29 , 232 ,
2012-07-05 21:27:32 , 350.0 , 800.0 , 75.0 , 52 , 29 , 232 ,
2012-07-05 21:27:33 , 350.0 , 800.0 , 75.0 , 55 , 29 , 232 ,
2012-07-05 21:27:34 , 350.0 , 800.0 , 74.0 , 60 , 29 , 232 ,
2012-07-05 21:27:35 , 350.0 , 800.0 , 75.0 , 75 , 29 , 232 ,
2012-07-05 21:27:36 , 400.0 , 800.0 , 74.0 , 67 , 29 , 232 ,
2012-07-05 21:27:37 , 700.0 , 800.0 , 75.0 , 79 , 29 , 232 ,
2012-07-05 21:27:38 , 750.0 , 800.0 , 75.0 , 71 , 29 , 227 ,
2012-07-05 21:27:39 , 750.0 , 800.0 , 75.0 , 73 , 29 , 227 ,
2012-07-05 21:27:40 , 700.0 , 800.0 , 76.0 , 70 , 29 , 227 ,
2012-07-05 21:27:41 , 700.0 , 800.0 , 75.0 , 67 , 29 , 227 ,
2012-07-05 21:27:42 , 600.0 , 800.0 , 77.0 , 71 , 29 , 227 ,
2012-07-05 21:27:43 , 600.0 , 800.0 , 75.0 , 74 , 29 , 227 ,
2012-07-05 21:27:44 , 600.0 , 800.0 , 75.0 , 73 , 29 , 227 ,
2012-07-05 21:27:45 , 600.0 , 800.0 , 75.0 , 71 , 29 , 227 ,
2012-07-05 21:27:46 , 650.0 , 800.0 , 74.0 , 68 , 29 , 227 ,
2012-07-05 21:27:47 , 600.0 , 800.0 , 75.0 , 70 , 29 , 227 ,
2012-07-05 21:27:48 , 550.0 , 800.0 , 76.0 , 70 , 29 , 227 ,
2012-07-05 21:27:49 , 500.0 , 800.0 , 75.0 , 72 , 29 , 227 ,
2012-07-05 21:27:50 , 650.0 , 800.0 , 75.0 , 78 , 29 , 228 ,
2012-07-05 21:27:51 , 650.0 , 800.0 , 75.0 , 77 , 29 , 228 ,
2012-07-05 21:27:52 , 750.0 , 800.0 , 75.0 , 69 , 29 , 228 ,
2012-07-05 21:27:53 , 650.0 , 800.0 , 75.0 , 70 , 29 , 228 ,
2012-07-05 21:27:54 , 650.0 , 800.0 , 75.0 , 78 , 29 , 228 ,
2012-07-05 21:27:55 , 650.0 , 800.0 , 75.0 , 74 , 29 , 228 ,
2012-07-05 21:27:56 , 650.0 , 800.0 , 76.0 , 77 , 29 , 228 ,
2012-07-05 21:27:57 , 350.0 , 800.0 , 74.0 , 76 , 29 , 228 ,
2012-07-05 21:27:58 , 750.0 , 800.0 , 76.0 , 83 , 29 , 229 ,
2012-07-05 21:27:59 , 750.0 , 800.0 , 76.0 , 82 , 29 , 229 ,
2012-07-05 21:28:00 , 750.0 , 800.0 , 75.0 , 79 , 29 , 229 ,
2012-07-05 21:28:01 , 700.0 , 800.0 , 76.0 , 71 , 29 , 223 ,
2012-07-05 21:28:02 , 850.0 , 800.0 , 76.0 , 79 , 29 , 223 ,
~1000 Mhz looks ok for such a 17W model but after a while it goes down. This is maybe some sort of throttling (temperature limit or power budget). If possible you could try lowering GPU/CPU voltage. Disabling CPU Turbo might increase the TDP headroom towards GPU as well. Are you using the newest driver?
Using the latest 15.26.12.2761 drivers.
I'm unable to disable the throttling features as the bios lacks those settings as this is an ultrabook, so I can't test that one.
1050mhz is the correct maximum speed for this one, but rarely does it ever stay there for long, It could potentially be the temperature but it often jumps around without the temperature having gone too crazy, as if it was thinking the game itself didn't need the performance and throttled down.

