Hi Vlad,

I converted my 850 to LED low beams a few years ago, and have since tried to
get more powerful replacements. The problem is that with higher power LEDs
there needs to be more massive heat sinks to dissipate the heat. Thus they
become too large to mount in the standard headlight assembly.
I don't know about the clearances in the your model, but here is a link to
an interesting (But pricey) solution where the entire lamp assemblies are swapped out.

http://www.xtralights.com/98-02-volvo-s70-high-energy-led-replacement-headlights-clear-pair

This place offers the HID lamps for $120 cheaper than the LEDs, but I'm not sure
if HIDs are legal in every state.

The good news is the above solution looks very tempting, but the price is up there. I can guess where these lights are made, and some hunting on the web
might find these lights at a fraction of their high price, you might search
www.dx.com, a company that I've found with a huge selection of LEDs and good prices. Here's one of their new offerings that's 1/2 the price I paid 2 years ago and 2-1/2 X more powerful.

http://www.dx.com/p/g5-5hl-h4-40w-4000lm-6000k-4-led-white-car-headlight-foglight-dc-9-36v-2-pcs-414400

The problem is that it may be too big physically. Klaus is right that you may need to modify the bulb out sensor.
(Not a big deal, I disabled the low beam section since LEDs should outlast the car)

Note you can always mount the Silver Star halogens , but they are only a little brighter and they are lucky to survive a year and keep the bulb out sensor busy!

If you do find a good LED headlight option, please post your results.

Bill