Pros/Cons of 2wd/4wd in Bots?

Basically, I have an H bridge capable of 1200 watts. (2x25 @ 24volts.) I didn't want to shell out for 500-600 watt motors until I had everything working, so I bought 2 250 watt motors for currie scooters because I found them on sale for $24/each. (versus at least $100 for a 500-600 watt.) Ive determined that these are not going to be powerful enough for my application, and now I am trying to decide between:

  1. using my 2 250 watt motors and buying 2 more 250 watt motors and running 4wd. I would collect 2 each of the 250 watt motors in parallel to my Hbridge. Total cost : about $55 shipped.

  2. buying 2 500 or 600 watt motors and running 2 wheel drive. Total Cost: over $200 shipped.

This seems like a no brainer to me, buy 2 more 250 watt motors, but I find I get into trouble when I buy stuff without asking questions about pros/cons first :P

Are there factors I am not considering? Thank you.

I would go for a 4WD just because you can do manoeuvres that a 2WD bot only can dream about :)