I too had the same dilemma as yourself but went for Galaxy S in the end.
The GPS fix is very easy to do, it worked for me anyhow. I'm in Ireland.
Here are the two fixes I tried:
http://www.youtube.com/watch?v=PJmLLIfcWCY
[FIX] Updated: GPS Tracking Issues (Optional FIX) For Stock Phones - xda-developers
One of them definitely worked, because after a couple of reboots it just started working.
as for lag fix, I have yet to try Official 2.2 but as these guys say it doesn't work, so your best option may be rooting and there's a lag fix available after that. However don't hold me responsible if you brick your phone.
Do a bit of research anyhow and you'll find what you need.
It is a bit of a pain in the ass that the Froyo update hasn't fixed these things, but I'd still rather the bigger screen of the Galaxy S for media etc, and the touchscreen is much better as well -
http://www.youtube.com/watch?v=hVlsRCMltDg
Also you get 802.11n wifi, as well as DLNA streaming (although allshare can be a bit buggy at times), it even had official wifi hotspot creation in 2.1 (which I believe is defunct now 2.2 is out, but still good for some users), and the battery life seems good too compared to my friend's HTC desire but I can't vouch for his activity on the phone.
Touchwiz is actually pretty good compared to sense, but you can replace it with ADWLauncher or LauncherPro if you want anyhow, so it's all good...
Did I mention you get the full version of Asphalt 5 free as well?