Hi Lee, how's things mate? Haven't seen you for a while!
The Caster has got some really good reviews from people who have been running them. The majority of things I have read have been written about the pro version but I am sure the same basic positives apply to the rtr aswell. The main drawback you will have is that the Sharks and modified FTX's will have the longer wheelbase and be 1:16th rather than 1:18th. The extra stability the Sharks will have means you will be a bit behind in the handling stakes. That said I am running a TamTech against Sharks and Carismas and loving every minute of it!
Have a look at some of the used Sharks coming up for sale aswell though, with LRP recently discontinuing them, there will definitely be some bargains available pretty soon.
You planning on running this at Formby?