I wouldn't bother til yours broke then go for v92, a little bit better, either way I wouldn't spend alot of money on a 56k. The technology is proven so a cheaper one should work just as well as an expensive one.
The difference between expensive and cheap is how much CPU they use to do the Demodulation and Modulating (hence MODEM). Softmodem - practically all 56k crap out there - are not true MODEMs because they only have the DTMF (ring tone) part in hardware to interface with the phone line, and the rest is all CPU. Then comes HCF HSF and a whole lot of other titles. This refers to how much hardware is on the actually card.
Expensive modems are external and are MODEMs not a cheap alternative which wastes CPU power.
As for protocols V90 is it. V92 is just a minor extension for handling call-waiting. You will not achieve any speed increase for a new modem.
Good modems (external, US Robotics) can retrain connection speeds up and down. Soft modems usually only go down - hence a spiral of death on a bad phoneline. So if you have a good modem and connect at 33.6kB on a 56k modem then you may not be limited by the initial handshaking and get better than 3K speeds.
So V92 is pointless and you will find that most modems can be firmware upgraded to the v92 standard because it is not hardware related.
There are just way to many 56k modems out there. Its a nightmare to get a decent one (maybe ACF2 chipset)
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My experience has been that softmodems are typically good enough for typical browsing. About the best you can hope for is about 6.5kb/s with software compression enabled. Even USB modems can put up a false impression that they are zippy.
The first place you see a huge difference in modems is when you game. For example, in Quake2, a softmodem averages about 245 ping, a USB modem maybe 300 ping, and a controller-based (aka hardware modem) will actually be around 175 ping. As a comparison, a good DSL or cable connection pings 50-100, and on a local network, you get about 10. Needless to say, I use a controller modem. Anything less results in poor performance.
I guess to answer your question, No, things haven't changed much. Since phone lines limit the connection speed, things can't get any better.
I've been using a USR External for years. It's a serial modem and is excellent. Recently, I have been trying an internal modem that is software based just to have less cables around the computer, but it isn't as good.