Toto Drake vs. UltraMax

Is there any functional or performance difference between the Toto Drake and UltraMax models? Or are they basically the same in two-piece and one-piece designs.

I'm looking to replace an older Kohler 3.5 gpf one-piece Rialto which overall had performed pretty well.

According to the specs in Terry's Report on Low Flow Toilets, the Drake is rated at 900 gram and is a 2 piece. The Ultra Max is rated at 700 grams and is a one piece unit. Anything over 500 grams is considered good, so it depends on your preference. Either will work well for you.