Am I class 5a or 6? Is there a significant difference when looking for transplant options? (Photo)

Based on your photos you are technically class 5A however I believe you are close to progressing fully to class 6.A lot of your treatment plan depends on your age,which you did not mention. I would recommend a complete evaluation by an experienced Hair Restoration surgeon in order to determine what is best for you.

The Norwood classification at a given time isn't as important as many people think for the following reasons:
1. It doesn't take into consideration the progression of hair loss, so if we are to use this classification, we should try to guess what class the hair loss is going to progress to. For example, a 20-year-old seemingly Norwood 3 patient may actually be progressing to a Norwood 6-7, thus the surgical planning should be done considering the class that will eventually occur.
2. The classification does not dictate surgical options. The assessment of surgical options is a very sophisticated process, including evaluating the patients donor capacity and the surgeons skills.
As a general guide, I would suggest using just three classes depending on considering many parameters; mild, moderate and advanced hair loss. You certainly have advanced hair loss and the treatment plan should be done accordingly.

Male Pattern Hair Loss can be classified according to the Norwood Hamilton Scale. This scale is often misinterpreted by patients as a progression measurement but, in reality, is a depiction of the distribution of hairs on the scalp that have DHT receptors. It therefore shows the area where a man is genetically predisposed to thinning or going bald. Whether or not you are genetically predetermined to have a 5a or 6 pattern of hair loss will only become fully apparent with time. With regards to the number of hairs available - this depends on the method of donor harvesting as well as the ratio and size of hair groupings within follicular unit grafts. With Strip FUT, the head size, scalp laxity and hair density will determine estimated follicular unit graft numbers. With FUE, head size, hair density and width of the safe donor zone will determine estimated follicular unit graft numbers but ease of extraction and transection rate will impact on actual number of hairs extracted.An experienced hair transplant surgeon who offers both methods of donor harvesting will be able to advise you after a thorough scalp examination. 

You have a troubling Class 5a pattern because the crown component seems to spread suggesting that it might be an early Class 6 pattern in the making