Go for the 170i. I am 6'1" and 185 lbs, and I find mine to be comfortable
plus the 170i engine will move you rapidly. check with Floyd at Vespa Marietta to see if he has any Specials or derals working at the moment.
Good guy to del with.
The performance of a Blackjack and the 150 Pamplona should be virtually identical except the Blackjack has upgraded (NCY) suspension and brakes. This improves overall handling considerably. The 170 with fuel injection should increase performance, but I didn't see a much difference in actual riding situations with my Blackjack and a friends 170. I think either would work. Depends on the deal.