From your last sentence in your post above, it seems that it is not a geometry question, but fine tuning your fit. I am always cautious when bike geometry, especially HA/SA comes into play on 2 similar sized bikes. Bike handling characteristics change as geometry changes and if your Felt is too aggressive from a handling point of view and you want a more laid back ride, then geometry changes are a benefit. If you love the way your Felt dives into corners and the overall handling, then the Vortec may be disappointing. You have to ride it to see if you like the way it rides.

If it is only riding position, you can get a shorter stem that has more angle to raise the handlebars. If you don't want a "riser" stem, or there is not one that will work, you can probably get an uncut fork and make up the head tube/stack differences between the Felt and Vortec.

As for you Princpia, I'm not familiar with the bike. From the few pictures I have seen, it looks similar to an older aluminum Cannondale. I ride a Cannondale and it is a stiff frame. Fortunately I am running a steel fork that does wonders.

John