Should NASCAR drivers have speedometers in the car?

In response to Sunday's race where Juan Pablo Montoya effectively lost the race that he had won all because of a pit road speeding penalty.

To preface this, for those of you that don't know, NASCAR cars do not have speedometers in them. They only have tachometers that display the engines RPM's. During practice sessions drivers and teams attempt to match up those RMP's with speed to set pit road speed, as well as before the race the pace car will drive at pit road speed so all of the drivers can get an RPM reading for what pit road speed is. One of the problems is weekend to weekend, when you change your gear set up for the different tracks the RPM association to pit road speed is going to change drastically, not to mention some tracks have 55mph pit road speeds and some as slow as 25-35. Some teams have attempted to place lights on the dash that remain green as long as the driver is within the limit for speeding on pit road. Juan Montoya is one such driver, yet he claims that all his lights stayed green and was not speeding. The NASCAR electronic timing elements say different.

Obviously one problem may be that as the race wears on and the engine runs hotter and is used up, it may have to run at a different RPM level for the same speed which would throw off a drivers judgment. Is this his fault if he believes he is doing everything right?

The second thing is, NASCAR allows a driver to go 5 miles over the speed limit without getting a penalty. But 5.01 miles over and you have to make a second trip to pit road under green (if the penalty was under green) which at many tracks can take you down almost a full lap. So the question arises: Should NASCAR start allowing cars to put Speedometers in them for pit road usage or should there be some other way they can accurately monitor the speeds in the same manner NASCAR does?? what are your thoughts?