I read the post about PAT.
Alignment seems to be important for SSD performance, so I will use PAT if someone can provide it (the free offer does not exist any more).
BTW, I have tried to do the right thing by using the align= parameter in diskpart.
But my original question about cluster size other than 4KB is still unanswered.
There is a section (in the pdf link below) on how block sizes can influence performance, which basically confers with what the white paper and Robert are saying.
The motivation for my original question is that I want to maximize the responsiveness of my W7 laptop.
So I think I have to optimize it for large program and data files being loaded, small ones will load quickly anyway.
I therefore generated my data and backup partitions to NTFS with 64KB clusters (unit=64k in diskpart parlance).
Despite many efforts, I did not succeed in changing the system partition's cluster size to anything greater than 4KB, neither before installation (diskpart), nor after installation (Partition Wizard Pro) which provides a "change cluster size" function.
The Partition Wizard Pro's error message indicated that my system contains compressed files, files which can only be held in 4KB clusters.
When I will do the next clean install, I will create a separate partition for the program files, partition which I can create with 64KB clusters.
Thank you for informing me about the alignment issue.
It turned out that my boot + system partition was not correctly aligned, even though I had used the diskpart align=1024 parameter.
I finally succeded by omitting the align= parameter, in other words, W7 does align properly without any help from the user.
Almost two years later, I finally was able to satisfy my curiosity.
I got a new laptop, with to different SSDs installed (not Intel though).
On five identical size partitions, except for the cluster sizes 4KB, 8KB, 16KB, 32KB and 64KB respectively, I ran CrystalDiskMark Seq and 512K random performance tests.
All indicated performance figures were within 1.5%, a difference which I consider to be smaller than the measurement accuracy.
And no trend in one way or another!
Conclusion: I formatted all my partitions with 4KB cluster sizes.