theretrofitsource is about the worst place to buy bulbs due to their high markup. Apparently, they also don't know what type of bulb 986/996 Litronics use.
The bulbs are D2S, not D1S.
HID bulbs are not high-tech anymore, so paying more than $10 per set is just foolish. Any aftermarket HID projectors likely run $10 bulbs (mine do) and they are very bright.
If you must pay more to feel more secure, you could spend 4x-25x more, but there is no need. Try the $10 set above and see for yourself. Worst case, you're out $10.
Stick with 5000k or below unless you like purply-blue lights.