Is the 9 series their super tiny/lightweight version? Only suggestion would be to check the speed at which it will output whatever the lights require (6v?), less of an issue when road riding but might be an issue if you're planning on doing a lot of mountainous "gravel grinding"
I just checked the graphs on SP's website, with 700c wheels the SP8 will output 6v at ~14km/h, with the SP9 it's closer to 18km/h. Like I said though it's more an issue to consider if off-road/gravel riding where your average speed will be lower.
Is the 9 series their super tiny/lightweight version? Only suggestion would be to check the speed at which it will output whatever the lights require (6v?), less of an issue when road riding but might be an issue if you're planning on doing a lot of mountainous "gravel grinding"