I use daylight tubes myself ("Northlight"), for colour matching purposes, but unless they've improved a lot in the last 20 years*, they do tend to be low output compared to more common fluorescents such as Pluslux. The reason is that phosphorescent discharge tubes tend to have sharp spectral lines, which is why technically you cannot give them a colour temperature. To get a good approximation to daylight the manufacturers have to mix a lot of phosphors together, and the overall output is lower in consequence.
The ones intended for high output are a lot better (3x or more in some cases), with the disadvantage that they're useless for colour matching.
So if you can get a high-output daylight tube, go for it, but if colour matching isn't very important, you'll get better illumination with a high output tube instead.
One final point: it may be obvious, but tubes emit light sideways. To get best illumination, if your workshop has a rectangular floor plan, align the tubes across the long axis, not along it. Also, painting the ceiling or rafters white will also pay dividends, even if the tubes have reflectors above them.
Cheers,
E.
*the last time I went into all this!