Our goal is to have rabbits that reach 5lb at 8-9 weeks.  Currently our rate is 10 weeks+ on average.  With our current stock the path to our goal requires time.  We save the best and fastest growing rabbits from our good breeders that exhibit the qualities we like: easy breeders, good mothering skills, good litter size 8-10. 
We recently retained our first rabbit from our own stock.  Our retained doe, Moonshine,  is out of Obilesk and Pocket.  She is a American Chinchilla and Californian cross.  Why we kept her: she is a solid brick, healthy, has a gentle temperament, and both her parents have been reliable producers of good size litters.  Most of her litter mates, which were bigger than her, unfortunately were bucks.  She reached 5 lbs+ at 10 weeks and has been gaining steadily ever since.  I just weighed her, at 4 months she is 8 lbs.  The best way to improve your stock is to select the qualities you want and keep kits with those qualities- the biggest of the big.

Besides genetics other things can effect growth rates:
1. Litter size.  If you have only 3-4 kits in a litter they will probably be born bigger and gain better as there are less nursing off one doe.  Litters of 11-12, the kits are often born smaller and they will be sharing the supply intended for 8 kits.  Good milkers can adjust for this but there still may be a longer grow out. 
2. Quality of feed.  Nursing does and litters should be free feed pellets.  Protein at 16% is minimum and 17-18% is often recommended as to better met their needs at these stages.  When you give minimal amounts of greens/hay, up to 10% should not interfere with the nutritional balance but more than that and you can mess with balance needed to grow and produce milk, there by decreasing the growth rate. 
3. Health and seasons.  The general health can effect growth rate as well.  If rabbits are sick or struggle with illness then their nutrient go to healing over growing.  Seasonal changes or extreme heat or cold can effect the growth rate and stress level of kits.  Limiting stress and having healthy stock is important. 
4. Cage size.  Like goldfish when over crowded a kit will take longer to grow.  So you should put 1-2 kits in a cage of 24x24.  More and you will decrease rate of growth.  It is also recommended to separate by sex so there are no mistakes, in case you sell or retain any of your stock.

Keeping records is essential in tracking the production of your breeding stock and the growth rate of your kits.  This will give you a foundation of selecting which stock to retain and which breeders are not performing well and need culled.  Starting out with the best stock you can get to your local climate is key, although bringing in excellent stock may be what is needed sometimes. 

This is the minimum that would like to be seen, close to what is on the chart of 1.05 oz daily gain. 
3wks = 1 lb
4wks = 1.5lbs+
5wks = 2 lbs
6wks = 2.5lbs+
7wks = 3-3.5lbs+
8wks = 4lbs+

The below chart is average daily gain calculated in weekly performance.  It is just an average guideline.

         1.05 oz  daily gain
week 1          7.35 oz
week 2         14.7 oz
week 3        1 lb 4 oz
week 4        1 lb 13 oz
week 5        2 lb 4 oz
week 6        2 lb 12 oz
week 7        3 lb 3 oz
week 8        3 lb 10 oz +
week 9        4 lb 2 oz+
week 10      4lb 9 oz
     1.23 oz  daily gain
week 1          8.61 oz
week 2        1 lb 1 oz
week 3        1 lb 9 oz
week 4        2 lb 2 oz
week 5        2 lb 11 oz
week 6        3 lb 3 oz
week 7        3 lb 12 oz
week 8        4 lb 4 oz+
week 9        4 lb 13 oz+
week 10      5 lb 6 oz
       1.41 oz daily gain
week 1          9.87 oz
week 2         1 lb 3 oz+
week 3         1 lb 13 oz
week 4         2 lb 7 oz
week 5         3 lb 1 oz+
week 6         3 lb 11 oz
week 7         4 lb 5 oz
week 8         4 lb 14 oz
week 9         5 lb 8 oz
week 10       6lb 2 oz+