First, I would like to say that I have been more of a runner than a bicycler, so am king of ignorant about bikes...

I just moved, and I now currently have an 8 mile (one way) commute to work. It is along a road that is 3 lanes each direction, 45 mph speed limit. There are many traffic lights; it is a commercial type area (restraunts/stores, some houses). Traffic is usually not too bad, most of the times traffic can easily fit into 2 or the 3 lanes. There is a sidewalk the whole way, but it is in pretty bad condition for a lot of it.

I am currently riding a Dahon Mariner (2007) that I picked up in college when I had to park over a mile and a half from my dorm. It has served me very well so far. I ride the sidewalks all the way there, averaging about 15 mph (including waiting on lights). Most the lights turn red with only 1 car at little side streets; since I'm on the sidewalk I just keep going. For the real intersections I actually wait for the light to turn green.

My issue is that once I get up to about 15 mph, I am starting to peddle pretty quick and would like to shift to a better gear. I spend pretty much all my time in gear 7 (out of 7), except for starting from a stop. It's gear inches are 34" - 92". I would like to go faster, but it is just too tiring peddling that quick for too long. I was able to get it up to almost 30 mph once on the street to cross an intersection, but I was peddling so quick it seemed that the chain wasn't even attached... >:0 The sidewalks also prevents going much faster, as they aren't in good condition.

I would like to ride on the road, but 15 mph is not going to cut it in a 45 mph zone, even if traffic can all get over. If I get a bike with a higher gear range, how fast can I expect to go? Would I be able to ride on the street? I am in pretty good shape because I run, but I am not a heavy bicycler (though am really starting to get into it! ) I am looking at bikes like the Dahon Matrix, Dahon Speed TT, and Dahon Cadenza, and speed TR. All these bikes go up to 110-125 gear inches or so. I hate being limited by by bikes gearing, so wouldn't mind getting one with gears higher than I would use and grow into it as I get better.

I am leaning towards the Speed Pro, as it is the fastest, but is also the most expensive. If I won't be able to go fast enough on the street and live, then the matrix looks the best as it has good shocks, and would be better on the "sidewalk"? The cadenza looks like a cheaper version of the Speed Pro (but with 26'' tires)? The speed TR looks like a more expensive version of the matrix? Maybe I should just consider a normal bike? I live in an apartment, so I take my bike inside. I also have a civic, and like to put my bike in the trunk. A normal bike wouldn't fit. I took my mariner to a trail once and did 50 miles on it. I haven't done this since because I was so sore in the rear after this. It would be nice if I could do this with my new bike. I would like to get into more bicycling and do some longer distance road stuff too, but don't feel comfortable doing this on my mariner...

I am single, so I can spend my money on whatever I want, but I just got out of college so don't have a ton of money. I can easily afford a $1000+ dollar bike (like the speed pro) if that is what would help me out, but I don't want to spend that kind of money if it would be a complete waste (aka, is the speed pro just for pros?)!

Please help! Sorry for the length...(and thank you very much in advance!!!!!!)