Not only will you not see any appreciable improvement in light performance, you'll heat up and eventually melt those notorious Volvo electrical connectors. The best premium lights produce higher and whiter output at stock rated....and they outperform overwatt lamps. (Some systems, like Razo, operate at higher watts and really do produce a lot of light, but they also create a lot of heat. A friend of mine put them in his Honda Oddity and warped one of his reflectors because of the heat. So be careful.)

Halogen and incandescent lighting produces heat, with light as a byproduct. You'd be better off doing an HID conversion. More light, less heat.
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David \\ (98 S70 T5SE Black, misc mods (mostly lighting), red calipers) (92 940GLE)