I just bought my 1965 Mooney M20E last month, and I love it. Lycoming IO360 fuel injected with 200 HP - 20 more horsepower over C model. E model is probably your best speed for your buck.
I'm 6'7", but pretty lanky - not wide. The legroom is amazing. It's a very comfortable 2 seater. I've had 3 people including me and it's tolerable for maybe an hour or so. The only way you'll do 4 is if people in the back are small kids. But for the two people up front, can't beat the legroom.
I file 148 knots and figure 10.5 gph on mine, but I'm still getting used to it.
Johnson bar takes a little getting used to, but it is a fool-proof system.
As for leaky tanks, yes, Mooneys have issue with them. You can do several things: do a complete reseal, install bladders or do a patch job. Depending on severity, it may not be necessary to do a full reseal, but be sure that a reputable shop does the work. I'm having Don Maxwell address my fuel tank issues.
For 45k, you're looking at short-body models C and E. You may find an F model in that price range which is a stretched E model (200HP fuel injected) with 10" added to fuselage of which your back seat gets 5" which now you're looking at a true 4 seater. Lower end J's usually start in 60's.
Also, if you go the Mooney route, have a Mooney Service Center do your prebuy inspection. They know exactly what to look for. It will save you lots of money in the long run.
Bottom line, you want speed and economy, can't go wrong with a Mooney.
Here is some reading for you:
http://www.mooneypilots.com/mapalog/M20C Evaluation/M20C_Evaluation_Report.html
http://www.mooneypilots.com/mapalog/m20e.html