When I purchased a Volvo S40 T5, I upgraded the low beams from H11s to modified H9s.
On the high beams, I went with the HIR conversion. I just changed one side and went out for a spin to see if there was an improvement. Hell YES ! I completed the other side and the amount of light compared to stock is well worth the cost of the bulbs. A HID conversion may put out more light but for high beams (where you may need instant lighting), the HIRs are the way to go.
This spring, I will be getting a HIR to replace my high beam on my Suzuki.
"It ain't no rocket surgery"-Keyf