Well, I'm biased but I think you should hold out for your Challenger. Easiest way to tell is, both cars side by side exactly how you like them - what keys do you grab first? What ever those keys are is the car you should go for. You'll be fine mate. My Dad is around 5ft-7" and over 60 and he'll be out driving his soon, they are pretty small cars IMO. Smaller than the new gen Chargers and 300Cs etc, in all dimensions, even weight (depending on donk). You'll be fine, the interior is quite confining and tight so it will suit a smaller driver like yourself. How do you plan to source your car? Wait it out in the UK and hope that one turns up sooner or later. Or, import one from the US of A?
I just typed out a whole reply and lost it, argh!
Anyway - yes, the Challenger is my dream car. But if it came down to that simple choice, it would mess with my head! In the end it comes down to money and availability. In a years time I expect/hope to have saved at least £10,000 towards a car. This is figuring on a basic salary here in the UK minus my expenses and being VERY conservative with my spending (I still live at home so at the moment am fortunate to not have huge bills to pay). So I don't really expect to find a Challenger that I want for that amount, although in reality a year is less than I am planning around. I would say in 2 years I'd likely have enough to start looking.
I guess the size thing concerns me - at the moment I drive a Ford Fiesta and it fits me perfectly. Headroom is just right - I look straight out the middle of the windscreen. I know the headroom in the Challenger is about the same (37.something inches) but because the seats are lower I'm not sure. That said, I know in Vanishing Point that Barry Newman looks like he's hunching inside the Challenger quite a lot of the time, and he's only about 6'. But that's besides the point - I really need to get to some shows and see these cars for myself.
In regards to the Mustang, it's a car that I could afford and I like it when it's painted like this:
Realistically, I could buy one of those here in the UK and paint it like that and do the interior all for under £10,000. I've started talking to some guys who live a few miles from me who are involved with Mustangs themselves, so it'll be good to see some 'in the flesh'. The Challenger will always be my goal - it just depends on the money at the time and how I feel. I see the Challenger as more of a long term thing - where as the Coupe would be my daily driver until I decide I want to sell it on and feel I have the space and time for a Challenger. That's the idea.
In terms of where - I'd hope to find one in the UK, or at least Europe, purely so I can see it. If not, I'd look toward anywhere that has one, and pay an independent inspector to check it out for me.
And yes, I would paint my Coupe like that one!