I have one, but can't remember when it was made. White's seems to have made a flurry of detectors for a space of time, some models seem to have overlapped, at points.
As near as I can remember, the Eagle Spectrum came out around '92 or so.
The current XLT is the E-series. The model before that is the Spectrum XLT. These models are electronically identical. The model before the Spectrum XLT is the Eagle Spectrum.
There differences between the Eagle and the XLT are huge, but the price difference is not. A good Eagle with hard case will sell for around $300.00 while the XLT will go for $350.00 to $400.00.
The Eagle Spectrum comes in a slimline case, which means it uses 4 'c' cell batteries. This makes the case almost twice as big as the XLT, which uses 8 'AA' batteries.
The LCD of the XLT has much higher resolution than the Eagle. This means the text is less pixelated, and much easier to read. This model also introduced the graphic icons that all the newer detectors use.
Processor speed is quite a bit higher with the XLT too.
Having said all that, the Eagle is still a good detector. If you have an opportunity to buy one at a very good price, I'd suggest taking advantage of it. If you should decide to upgrade later, the Eagle will make an excellent backup detector.