Pacific 22 RIBs
As far as i am aware the new MkII's have a completely new hull design as well as the waterjet and new inboards although i am not sure if these are actually larger than the standard MKI engine as the service speed is still only 22kts.
Also, the MKII's have self righting capability, a single point lifting system and more storage. Correct me if im wrong but i think they may be longer too!
Give a standard MKIa go as upgrading to a MKII is impossible. I think youll be extremely impressed with its seakeeping - they havent got such a reputation for nothing!
Also, no ballast tanks. The RNLI only had them installed to counteract a stern heavy design i believe.
Hope this helps although i am not sure if it is all 100% factual - only basing it on what i have been told.