I went with new Depo 2003/2004 Jewel assemblies. Unbelievable headlights! No modifications, perfect fit.

The Silver Stars that I put in our 850s were quite a bit better than the standard bulbs AND they draw 5 watts LESS than standard Volvo bulbs - no potential damage to your wiring or housings.

They now sell two versions - cheaper at Walmart.

They lasted as long as Volvo bulbs - 2 to 3 years or so. I carried the old bulbs as spares.

Give them a try, I found them to be well worth the money.

I used the Silver Stars in my old 740, they were a little brighter, but that comes with a short service life expectancy. They don't last long.
Now I have some early LED replacements for my 850 low beams, they are brighter
than the standard filament bulbs, but require the standard bulb out sensor to be
disabled (A simple jumper soldered in)

There's newer LEDs all the time but one of the problems is that high power LEDs
need to dissipate some heat and require heat sinks that become bulky.

A few of the newer 9005 replacements would not fit in the 850 headlight housing
because the heatsink protruded too far to the rear so that you can't put the cover on. Who knows if the 850 and S70 headlight housings are identical?

You can look at this offering: 3200 lumens!
http://www.dx.com/p/ax-4hl-9005-3200lm-9005-36w-3200lm-6500k-cree-custom-made-white-car-headlight-dc12-24v-2pcs-347881

It's more than double the light output of my LEDs, but will it fit in the lamp housing?

Here's their 9005 headlight selection:
http://www.dx.com/s/auto+led%2c+headlight%2c+9005

This might be good if it will fit in the housing. 4000 lumens!
http://www.dx.com/p/9006-40w-led-car-headlight-daytime-running-light-white-6000k-4000lm-4-cob-dc-9-36v-2pcs-412236

I'd stay away from the 100 watt unit. an energy hog.
Here's another option: (But will it fit?)
http://chromeglow.com/products/headlights-and-passing-lamps/bulbs/led/9005-9006-motorcycle-or-auto-led-headlight-bulb/

Here's one that might fit
http://www.ebay.com/itm/9000LM-90W-LED-Headlight-Kit-H7-H8-H10-H11-9005-9006-9145-9003-H4-H13-9004-9007-/281721341025?hash=item4197e68461:g:pDcAAOSwKrhVe7fk&vxp=mtr

This one didn't fit the 850
http://www.ebay.com/itm/2x-9006-HB4-9006XS-60W-Cree-5200LM-White-LED-Headlight-Conversion-Kit-Light-Bulb-/261933366916?hash=item3cfc71fe84:g:TGMAAOSwDNdVhDEI&vxp=mtr

This one looks tempting: (But will it fit?)
http://www.ebay.com/itm/9000LM-90W-LED-Headlight-Kit-H7-H8-H10-H11-9005-9006-9145-9003-H4-H13-9004-9007-/281721341025?hash=item4197e68461:g:pDcAAOSwKrhVe7fk&vxp=mtr

Brighter bulbs just produce more glare. I used a set of E code lenses with the stock bulbs and was thrilled with the extra light on low beam, and high beam was like daylight. I did have to put a small patch of electrical tape on the left lense to keep the entire left light flat.

The E codes will make you readjust the headlights, the stock setting will be too high.

https://www.fcpeuro.com/products/volvo-e-code-headlight-lenses-850-v70ecodekit

Remember, never touch the reflective area inside the headlight. It cannot be 'cleaned'.
--
Keeping it running is better than buying new

Not to rain on a parade or 2 but the Sylvania's I bought had a chart on the back. They were brighter but they burned out faster. I had an s60 that always seemed to be burning out bulbs. I returned to OEM, got a 1 year guarantee and no burn outs ever again. Sorry 'bout that.