In terms of reliability I don't think the Rover would be a good choice, in the R500 Caterham with 230hp the engine is good for 5 -10K miles before a rebuild. It is really at it's limit in the mid 200 hp range.
I had a ride an a Caterham R500 and it was unbelievable, the claim of 0 - 60 in 3.5 seconds seems understated according to my built in accelarameter. The handling and power to weight of the R500 is amazing for a street legal (at least street legal in the UK) car. The R500 refers to the fact that this car has 500hp per ton of weight, how many cars have that? So I guess the R600 is 600hp per ton?
Yea there are a number of R500 owners on the Lotus 7 forum out of the UK, depending on driving style the engine requires a lot of maintenance. Here is the link to Caterham and the R500, a 1.8 liter Rover K series with 230 hp! http://www.caterham.co.uk/showroom/index.htm
Just page down on the site a little to Superlight and it's specifications. Oh, I bought a set of the magnesium wheels that come on the Superlight, 8 pounds each!