Hi Taz, assuming your Envy 17 comes with 2230 and you'd like to upgrade to either 6235 or 7260, both of these cards have the same form factor with your 2230 which should fit on your laptop. In terms of functionality, 7260 gives you more flexibility in connecting to different wireless standards from 802.11 ac/a/b/g/n. Sharing the link on where you can find the comparison between models:
In terms of compatibility, suggest to contact HP on which wireless model has been tested to avoid usage problem.
Moving your thread to wireless forum, members on the forum might be able to provide additional info on your inquiry
As was mentioned by Vince_intel, the 3 adapters are available in HMC form factor. The Intel® Centrino® Advanced-N 6235, Dual Band and Intel® Dual Band Wireless-AC 7260 have additional features not available in the Intel® Centrino® Wireless-N 2230, Single Band.
We would like to mention that Intel recommends you contact the manufacturer, vendor, or the source where you obtained your computer regarding availability and support for upgrades of the various Intel wireless adapters. The wireless adapter should only be installed by the manufacturer or its authorized representative.
Replacing an adapter with a different (incompatible) type of adapter may cause errors at boot time, problems during the installation process, or unexpected behavior during operation. In some cases using an incompatible device may cause hardware damage to the adapter, the laptop or both. Adapter replacement may even have legal implications due to country specific regulations.
For more information, please check the following documents: