This paper may give you some idea: http://occmed.oxfordjournals.org/content/54/2/76.full.pdf+html

Inorganic lead compounds are the most toxic and predominant forms of lead in the environment. The available data on organic (i.e., alkyl) lead compounds indicate that some of the toxic effects of alkyl lead are mediated through metabolism to inorganic lead and that during the combustion of gasoline containing alkyl lead, significant amounts of inorganic lead are released to contaminate the environment. By far, most lead at hazardous waste sites is inorganic lead. The limited data available on alkyl lead compounds indicate that the toxicokinetic profiles and toxicological effects of these compounds are qualitatively and quantitatively different from those of inorganic lead. For more details have have attached "Toxicological Profile of Lead (ATSDR, 2007)

Hi, 

I do not think that organic lead is less harmful than inorganic. Organic lead in the same manner as organic mercury can readily pass through the so-called "haematho-еncephalo barrier" and cause injury to the brain. Read more in enclosed link.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1567786/

You may try also these links (especially the last one - there is a discussion of toxicity of organic lead vs inorganic lead):

http://www.researchgate.net/profile/Aristidis_Tsatsakis/publication/7571843_Lead_toxicity_update._A_brief_review/links/0912f50dd920823e05000000.pdf

http://exposicionesvirtuales.com/so_images/7597/leadandmercury.pdf

http://onlinelibrary.wiley.com/doi/10.1046/j.1365-2125.2002.01580.x/full

https://www.qatar-weill.cornell.edu/research/faculty/busselberg/publications/Occurence,%20use%20and%20toxic%20effects.pdf

You must take into account that the mobility of organic lead is higher than inorganic lead. Thus, although they may be inorganic forms of lead with higher toxicity, the absorption of organic lead is faster.

Article Lead toxicity update. A brief Review

Toxicity levels are mostly determined by considering bioavailability - where aspects such as speciation and mobility of a contaminant or pollutant are concerned. As such, kindly if you find this an interesting angle to pursue - read the following paper that carried out on the basis of remediating lead contaminated soils using ameliorants an overall preview of  lead (hope it will be helpful!)

- Edmond Gatima, Mwinyikione Mwinyihija and Ken Killham (2006). Determination of adsorption efficiency related to red earth, Bone meal and Pulverised Fly Ash as ameliorants to lead contaminated soils. International Journal of Environmental Science and Technology. Vol. 3 (3):269-288. available at; 

http://www.ijest.org/_action=article&vol=3&issue=17&_is=Volume+3%2C+Number+3%2C+Summer+2006%2C+Pages+203-325.

Read the discussion of the paper.

I  think that organic lead is this same toxic metal as inorganic.  Read more in enclosed link. See also publication: Khan M.Z., Szarek J., 1994.

Effects of concurrent oral administration of lead, selenium or monensin

on hepatic porphyrin levels in broiler chicken during subacute toxicosis.

Journal of Veterinary Medicine, Series B - Zentralblatt für Veterinärmedizin Reihe B, 41: 77-82.

I agree with

Józef Szarek, that organic lead is same toxic metal as inorganic.

Yes organic pollutant is less toxic as they can undergo degradation unlike the inorganic pollutants which are non-degradable and can last for ages