I'd still get a 9500 Pro, given the choice. In fact, I bought one today for a system just after reading the 9600 Pro reviews.
A heavily overclocked 9500 Pro will still be faster... I'd be glad I made the right choice if I were you!
If you think about it, you only need to O/C a 9500 Pro to 300MHz to match pixel fillrate of a 600MHz 9600 Pro. The R300 has a hierarchial Z-buffer as well, which gives it a huge memory bandwidth advantage (per clock).
My monitor maxes as 1024x768 as well (LCD), and I can play whatever I want with great performance (the Tbred helps me a little I'm sure). I think it will be much better than the GF4 MX you had. If you get the 128mb version, see how well it OCs. Many of these can do an extra 25mhz on the ram.
I've been so pleased with my 8500LE that I haven't even considered replacing it. This is from a guy who's upgraded his CPU twice and his motherboard once in the past year!
Give what you cannot keep to gain what you cannot lose.
I have been using the Radeon 9100 (128mb) in my system builds lately which is just a 128mb 8500 renamed (was using 128mb GF4MX440's) and the 9100 is a great card, I built my kids an Athlon 1800XP with the 9100 and to be honest it plays games (UT and UT2003 mainly) nearly as well as my P4 2.85 with Radeon 9700 Pro.