You can put tons of miles on these kinds of bikes but the seating position is just not very efficient when it comes to climbing hills and standing to pedal isn't as easy (or even possible on some of the stretch cruisers) They just aren't good for hilly areas. The geometry of the Nirve bikes is a little more suited to hard riding if thats your plan.

I ride a Kustom Kruiser Slick Daddy and I've put buttloads of ultra comfy miles on it...it just sucks on hills. Even in 1st gear on a 42/19 (3 speed IGH)...it'll make it up most hills, it will just be really slow going.

**edit**

Those Felt Cruisers are really really cool. I like the 3 speed "M.P" with the integrated rear rack and the "1903" with the springer fork

...I'd like the MP, with a springer fork and the "1903" handlebars.and a 7 speed hub.