I dont know about the flashing type - do you have a link for them??

Im assuming that the standard LED's have a delay on lighting up due to the series resistor on them. Flashers would have to negate this.

I have access to a whole host of LED's in my line of business - might be worth seeing if i can come up with something

These are the ones I was looking at from RTBB  (#89's).  I don't have specs for them but if they are brighter and sharper than the existing #89's then I will give them a go (just on topper to start with)

http://www.rtbb.com.au/catalog/index.php?cPath=22_119_121