I have the Xenarc in a bmw cabrio. I switched to the high-bright model and it's slightly better, but still washes out in full sun, obviously. You just can't expect a screen to put out more light than the direct sunshine - you're dreaming.
That being said - it doesn't take away from a carpc setup. You're not staring at the screen while driving anyways - or rather you shouldn't be. the gps calls out directions, you can hear the music, so what's the big deal? When you're cruising around in the full sun in a cabrio, don't you usually just turn it up and cruise?
Since you have to touch it to do anything, your hand shadows it as you reach for it, and you can see what you need to see. I strongly recommend you come up with a way to keep the steering wheel controls (either ir or i-bus), or have some other easy controller so that you can at least use the volume and skip without looking at the screen.
Your only alternative is daylight-viewable marine monitors, of which there are many, but they will kick your *** at night and will cost more than a few carpc setups combined.
if you drive a cabrio in a sunny place and can afford a carpc, LIVE WITH IT!
).
) and do some tests with my sff desktop and an inverter. I can always sell it afterwards!!!
for "sunlight readable lcd". One such hit is Vartech Systems which has several models: 
Linear Mode
